Activated eosinophils release toxic cationic proteins that can damage tissues and kill parasitic organisms. Other products of eosinophils increase microvascular permeability and recruit inflammatory cells to tissue sites, thus having a major impact on the pathophysiology of eosinophilia-associated diseases. For this reason, the factors that regulate eosinophil function are of considerable importance to immunology and medicine. Earlier studies showed that LPS-stimulated monocytes or PMA/LPS- stimulated U937 cells produce a factor that enhances eosinophil cytotoxic function in vitro. This factor (ECEF) has now been purified. A partial amino acid sequence determination suggests that ECEF is a novel monokine. ECEF-specific antibody has been produced in rabbits. The proposed research deals with the structure and biological functions of ECEF. The molecular cloning of the cDNA encoding ECEF is planned in order to determine the primary structure of ECEF and to produce quantities of genetically-defined ECEF for functional studies. cDNA and monoclonal antibody probes and peptide mapping will be used to compare the structure of natural ECEF to recombinant ECEF. Conditions that induce monocyte synthesis and release of ECEF will be studied. The production of ECEF by peripheral blood monocytes and tissue monocytes in eosinophilic granulomas will be analyzed for mice and human subjects with schistosomiasis. The mechanism of action of ECEF on eosinophils in vitro will be studied, with particular emphasis on the threshold of activation stimuli and rates of secretion. The effects of ECEF on other types of inflammatory cells will be evaluated, using functional and receptor binding assays.